The present invention relates to telephone equipment and in particular, to telephone equipment for providing an incoming ringing signal to the proper party on a party telephone line. In particular, the present invention relates to a programmable selective ringing circuit for party telephone lines wherein provision of the ringing signal to the proper party is accomplished by polarity decoding of the incoming ringing signal.
Various schemes are known for the decoding of ringing signals on party telephone lines. The present invention relates to a system wherein decoding of the ringing signal is performed by determining the polarity of the talk battery signal applied to the ring and tip telephone lines upon which the ringing signal is superimposed.
Now that the telephone industry has become deregulated, it is essential to provide a device external to a user's telephone, for use on a party telephone line, for properly decoding a ringing signal on that party telephone line. The reason for this is that telephone customers may now purchase their own telephones and install them. In the case of party lines, a normal telephone instrument would not be able properly to decode the encoded ringing signals on the party telephone line. Accordingly, an external device is necessary to be installed in series with the telephone instrument so that only those ringing signals intended for that particular telephone will be received by that telephone.